Figure 5.

Match Any and Match First have the same trial structure. (A) Schematic example of three consecutive trials: a four-image sequence, followed by a six-image sequence, and then a four-image sequence. Trace indicates timing of image onsets and offsets, with breaks representing the interval between trials. In both tasks, the test image (last image in each sequence) always matches a previously presented image; test recency quantifies when the test image was last presented in terms of sequence index. The correct response at the end of each trial depends on whether the test matches a sample (“yes” correct) or distractor (“no” correct). In Match Any, each trial contains a series of sample images and ends with a test image, which matches either a sample from the current trial or a distractor that was last viewed in a previous trial (a preceding distractor). In Match First, only the first image is a sample and the images between the first and the test are intervening distractors. In Match First, the test image matches a sample, an intervening distractor, or a distractor that was last viewed in a previous trial. For Match Any, the correct responses to the three trials would be yes, yes, no, whereas for Match First, the correct responses to the same three trials would be yes, no, no. (B) Schematic of images and instruction targets during an example eight-image sequence. The trial begins when the monkey touches a bar, which triggers the presentation of a red instruction target (red square), before a trial-start instruction target (checkered circle) is presented and removed. While the red target is on, up to eight images are presented and then removed in sequence (filled bullet [•] indicates an interval with no image; total sequence duration up to 16 sec). The red target turns green to indicate that the last image viewed was the test image. A “yes” response is registered when the monkey releases the bar during the 1-sec-long green target; a “no” response is registered when bar release is delayed until after the green target disappears. Correct responses are rewarded with juice or water. Incorrect responses result in a 4-sec to 30-sec time-out. A blue target appears after a response has been made and remains on-screen throughout the feedback (whether reward or time-out). (C) Timing of actions, images, instructions targets, and feedback.